How to Isolate Ytterbium from Minerals?

As an even-numbered lanthanide, in accordance with the OddoHarkins rule, ytterbium is significantly more abundant than its immediate neighbors, thulium (Tm) and lutetium (Lu), which occur in the same concentration at levels of about 0.5% each. Ytterbium is often the most common substitute in yttrium minerals. In very few known cases/occurrences ytterbium prevails over yttrium, as, for example, in xenotime-(Yb). A report of native ytterbium from the Moon's regolith is known.

Figure 1. Keiviite-(Yb), Yb2Si2O7, tiny white crystal grains less than 0.4 mm in fluorite, CaF2.

It is quite difficult to isolate ytterbium from other lanthanides because of its similar properties. Consequently, the process is rather long. In a first step, minerals such as monazite or xenotime are dissolved into various acids, such as sulfuric acid.

Ytterbium can subsequently be isolated from other lanthanides by ion exchange, as can other lanthanides. The solution is applied to a resin, which binds the various lanthanides in different ways. This is subsequently exposed to various complexing agents, and because of the different bonding types exhibited by the different lanthanides, the compounds can be separated. Ytterbium is isolated from other REEs either by ion exchange or through reduction with sodium amalgam. In the latter process, a buffered acidic solution of trivalent (13) REEs is reacted with a molten sodiummercury alloy, which results in the reduction and dissolution of Yb31. The resulting alloy is then reacted with hydrochloric acid (HCl). The metal is separated from the solution as its oxalate and subsequently decomposed to its oxide upon heating.

Finally, the oxide is reduced to metal by heating in the presence of lanthanum, aluminum, cerium, or zirconium in high vacuum. The metal is purified through sublimation and then collected over a condensed plate.